Rotary stencil film cutter



Oct. 17, 1950 P. N. RICE 2,525,828

ROTARY smucn. FILM CUTTER Filed Nov; 15, 1946 INVENTOR. PEP/V7762 A! 5/62 ///.s irrae/vsya Patented Oct. 17, 1950 UNITED STATES. PATENT OFFICE ROTARY STENCIL FILM CUTTER Prentice N. Rice, Dayton, Ohio Application November 13, 1946, Serial No. 709,634

(01. 29103) (Granted under the act of March 3, 1883, as

8 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to a routing tool and, more particularly, to a rotary tool or bit suitable for cutting designs on film stencils of the type used in the silk-screen printing process.

In the past, it has been customary to prepare film stencils of the aforementioned type by placing the stencil over the design to be reproduced and then cutting the film around the outlines of the design with a sharp knife, care being taken not to cut through theglassine paper backing of the film. That part of the film which is to be removed from the stencil is then stripped off of the paper backing, and the stencil is then ready for adhering to the silk screen.

This method of cutting stencils is a. difficult and exacting process, since the knife must. be handled in a very skillful manner in order to produce a stencil having smooth, unbroken outlines. The stripping of the film from the backing is also a delicate and time-consuming operation, since extreme care must be taken not to nick the edges of the film or to break through the lines of the design when the film is lifted up with the point of the knife.

It is therefore an object of my invention to provide a novel typeof rotary cutting tool.

Another object of my invention is'to provide a routing tool which will facilitate the cutting of stencils and render this task simpler and easier to perform than at present.

A further object of my invention is to provide a film stencil cutting tool which will cut a clean swath through the film layer of the stencil but which will not cut through the paper backing thereof.

still a further object of myinvention resides in the provision of a router having a peripheral cutting edge or lip .followedby. ascraping edge and a riding surface. These three elements are combined to produce a cutter which, asit rotates, makes circular or crescent-shapedcuts in the film layer and then removes the cut pieces of film from the paper backing so as to produce a sharply defined track or path through the film layer. The cutting lip is prevented from cutting through the paper backing by virtue of the riding surface which rests upon the surface of the paper backing and thereby limits the cutting action of the lip to the film layer.

With these and other objects in view which will become apparent from the followingdescriptionpthe invention includes certain novel feaamended April 30, 1928; 370 O. G. 757) tures of design and combinations of parts, the essential elements Of which are set forth in the appended claims anda preferred embodiment of which is hereinafter described with reference to the drawings which accompany and form a part of this specification.

In the drawings:

Figure 1 is an end view, greatly enlarged, of a routing tool designed in accordance with my invention.

Figure 2 is a front view of the tool shown in Figure 1.

Figure 3 is a side view of the tool shown in Figure Figure 4 is a view illustrating the mode of operation of the routing tool shown in Figures 1-3.

Figure 5 is a view showing one type of hand tool with which the routing tool shown in Figures 1-3 may be used.

Figure 6 is a view showing a portion of a fiexible cable type of tool with which the router previously illustrated herein may be used.

The constructional details of a router embodying the principles of the present invention are clearly shown in Figure 1-3, inclusive. As illustrated in these enlarged views Of the tool, the router is formed by grinding or otherwise fashioning an inclined face l2 on the end of a piece of round tool stock in so as .to provide a sharp peripheral cutting edge or lip [4 on or near the diametral line yy. When the tool I0 is revolved in the direction of the arrow :1: and held against a piece of film stencil, the edge M will make a circular cut in the shellac or lacquer film layer of the stencil.

Located just ahead of the cutting edge I4 is a pressure edge I6, which exerts a downward pressure on the film or other material being cut in advance of the peripheral cutting lip l4, thereby aiding the latter in making a clean. sharp cut in the film. As shown in Figure 4, the cutting edge -|4 will make a series of crescent-shaped cuts in the film layer 20 as the tool is fed thereacross, and a corresponding series of crescent-shaped chips I 8 will be removed from the paper backing material 22 of the film stencil. The cutting action of the edge [4 will be improved by the downward pressure exerted by the pressure edge I6 on the film 20 just in advance of the cutting edge. e

As shown in Figure 3, the face I2 is ground at an angle A with respect to the longitudinal axis of the routing tool Ill. While it has been. found that an angle A of 52 degrees is suitable for use on most types of films, this angle may be increased or decreased somewhat in order to alter the cutting characteristics of the tool. For examples, as the angle A is increased, the peripheral cutting edge I4 becomes less acute and the tool will not bite into the film as readily as with a smaller and more acute angle, thus providing a router which is less sensitive and which is better suited for cutting the softer and more fragile types of films. Conversely, as the angle A is decreased, the cutting edge I4 becomes more acute so as to produce a tool of increased sensitivity and one which will cut into tough films with the application of very little pressure.

As illustrated in Figures 1-4, the inclined face [2 is joined by a fillet 24 with a substantially vertical face 26, which extends across the end of the tool in the direction of the face I2. The face is spaced somewhat to the right of the diametral line yy as shown by the dimension m in Figure 1. This distance should preferably not exceed, .20 r, where r is the radius of the tool stock- H). The upper end of the face 26 terminates in a substantially horizontal riding face 28, which has a curved scraping edge 30 on the side approaching the film as the tool revolves in the direction of the arrow ac. This edge tends to scrape and curl up the film from the backing material 22 after ithas been cut by the lip [4.

The rear edge of the riding face 28 is approximately straight, as shown at 32 in Figure 1, and this edge, together with edges 34 and 36, bounds a triangular-shaped clearance face 38, formed on the rear side of therouter.

The riding face 28 should preferably have a length'h. (Figure 1) in the radial direction of at least 20% of the diameter of the tool stock it, though in the case of very small sizes of the tool, this length may be. increased to as much as 40% of the diameter.

As shown in Figure 2; the face 33 makes an angle B'with respect to the horizontal so as to provide an ample amount of clearance behind the riding face 28. Although the angle B shown in Figure 2 is in the neighborhood of 40 degrees, this value may be varied considerably without adversely affecting the performance of the tool.

Bounded by the face 2'6, the edge 36 and the peripheral surface of the tool stock I0, is a further clearance face 40. As shown in Figure 3, the edge 36 makes an angle C with the horizontal so as to provide clearance behind the riding face 28 in the radial direction. The angle C shown in thedrawing is approximately 20 degrees, but this value may be increased or decreased by six or eight degrees without interfering with proper operation of the'tool. As also shown in this figure, the riding face 28 may be inclined slightly from the horizontal in a radial direction as shown by the angle E so as to provide a slight amount of clearance at the inner end of the riding face 2% and so prevent scuffing of th backing mate rial 22 by this part of face 28. The angle E may vary from to or degrees as may prove desirable for the particular type of material being worked on.

The manner in which the router may be used in cutting stencils or similar materials is shown in Figure 5, where the tool 5!! is secured'in the chuck of a conventional type'of rotary hand tool 42, which is manipulated in the hand of the operator so as to make a cut of any desired shape in the layer of film overlying the backing material 22. One such cut is shown at 44 in Figure 5.

An alternative. method .of operating the router for cutting stencils or performing similar work is shown in Figure 6, where the tool 10 is shown fastened in the chuck of a handpiece 46 mounted on the end of a flexible shaft 48 adapted to be rotated at high speed by a motor (not shown). Whatever the form of drive utilized for operating the tool, its speed should preferably be in the nature-of 10,000 R. P. M. or greater, so as to enable fairly fast cuts to be made without exceeding the ability of the tool to cut and remove the film from the backing material.

The operation of the tool is as follows:

As the tool is rotated in the direction of the arrow, the cuttin edge l4 follows the pressure edge I6 and makes a circular cut in the film or similar material 20. The cutting action of the edge [4 is controlled by the riding face 28, which bears against the surface of the backin material 22 and prevents the edge 14 from cutting into it. The riding face will not prevent the edge [4 from cutting into thefilm, since the lattermaterial is relatively softand delicate and. therefore unable to withstand the pressure. of the riding face 28 and the action of the scraping edge thereon.

The backin material, however, is a relatively tough and fibrous substance. which will support the face 28 thereon and prevent any further cutting of the backing material by the edge. l4..

As the router is moved: across the film, the cutting edge will make successive circular cuts in the film material lying in front of it and will therefore remove crescent-shaped bits of film [8. as

shown in Figure 4 from the stencil material. The routingtool should preferably be held with its axis approximately perpendicular-to the plane of the work, although the tool has been so designed as to permit-considerable latitude in this respect, thereby reducing thedegree of skill required for its use.

While the'tool has beendesigned'primarily for use with film stencils of the type used in the silk screen process, it will be appreciated that it may be used for routin out-designs in any similar laminated material without departing from the scope or spirit of my invention.

Having thusdesbribed my invention, what I claim as new and desire to secure by Letters Patent is:

A rotary routing tool. comprising a substantially cylindrical bit provided on one end thereof with a, faceextending diametrically across the .end ofthe bit and inclined to the axis of rotation of the bit so as to formv a single, sharp peripheral lipon one side of the bit, a substantially fiat surface extending radially inward from said lip and located on approximately the same level therewithfor supporting the endof the bit on the work and controlling the cutting action of said lip on the work, and. ascraping. edge formed along theforward edgeof said surface for assisting the lip in removing material from the work.

2. A rotary router for cutting film stencils of the typeused in the silk screen printing process, comprising a bit having an end fac on which are provided a cutting edge, a, riding face situated just behind said cutting edge and so located with respect thereto as to prevent said edge from cutting through thebacking material of said stencil, and a scraping edge lying immediately in front ofsaid riding surface and just behind said cuttingedge for removing the film from the backing material of the stencil after it has been cut by said cutting edge.

3. A rotary tool for cutting film stencils Of the type .usedn he. s lk. creen; printin p oc ss.

comprisin a bit on which are provided a peripheral cutting edge, a flat riding face following closely behind said cutting edge as the cutter rotates, said face being located in approximately the same plane of rotation as said cutting edge so as to prevent said edge from cutting through the backing material of said stencil, and a scraping edge lying immediately in front of said riding face for removing the film from the backing material after it has been cut by said cutting edge.

4. A rotary routing tool as defined by claim 1 wherein said surface is inclined slightly in the radial direction with respect to the plane of rotation so as to provide a small clearance at the inner end of said surface.

5. A rotary routing tool comprising substantially cylindrical bit adapted for rotation about its longitudinal axis, a substantially semi-circular face on one end of said bit, said face being inclined with respect to one plane passing through the longitudinal axis of the bit and perpendicular to a second plane passing through the longitudinal axis of the bit and lying at right angles to the first plane, a sector-shaped face lying substantially parallel to said semi-circular face but offset outwardly therefrom along the longitudinal axis of said bit, a third face disposed at right angles to said semi-circular face and extending in the direction of the longitudinal axis of said bit for connecting the latter face with said sector-shaped face, a riding face lying substantially in the plane of rotation of said bit and extending inwardly from the outer end of said semi-circular face to the outer end of said sector-shaped face, and a cutting edge formed by the intersection of said riding face with said third face. i

6. A rotary routing tool as defined by claim 5 wherein said semi-circular face is inclined at an angle of from to with respect to the firstmentioned plane.

7. A rotary routing tool as described in claim 5 wherein said riding face is inclined "with respect to the plane of rotation in the radial direction so as to provide a clearance at the inner end of said face.

8. A rotary routing tool as defined by claim 7 wherein said riding face is inclined in the radial direction at an angle of approximately 5 with respect to the plane of rotation.

PRENTICE N. RICE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,789,793 Wedhorn. Jan. 20, 1931 1,907,880 Royle May 9, 1933 2,273,624 Campbell et al. Feb. 17, 1942 

